In a mobile communication system, for saving power consumed by a mobile terminal, the terminal may stop receiving some signal from a base station serving the terminal, which is called as “discontinuous reception”. If the terminal is in the discontinuous reception mode, a time period, during which the reception of the signal of the serving base station must be kept, is called “active time”, the time period except for the active time is called “idle time”. As shown in FIG. 1, the terminal does not receive some signal from the serving base station during the idle time. Of course, the terminal may perform other operations, such as measurement of a neighboring cell, during the idle time.